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Electric field in presence of dielectric between the two plates of a parallel plate capacitor is given by,

\(E=\frac{\sigma}{K \varepsilon_{0}}\)

Then, charge density

\({\sigma=K \varepsilon_{0} E}\)

\({=2.2 \times 8.85 \times 10^{-12} \times 3 \times 10^{4} \approx 6 \times 10^{-7} \,\mathrm{C} / \mathrm{m}^{2}}\)